1. Field of the Invention
The present invention relates to radar systems and, more particularly, to Doppler radar systems for tracking targets in high clutter.
2. Related Art
Numerous Doppler radar systems including Doppler processing techniques are available. For example, U.S. Pat. No. 4,137,532 to Taylor, Jr. et al describes a Doppler radar system which has a variable interpulse period (VIP) filter bank to suppress echoes from terrain, rain and chaff. Each filter of the VIP filter bank suppresses a designated frequency band with a width being a large fraction of 1/Tav where Tav is the average period between data samples. The VIP filter bank has seven individual filters. Filter numbers 1 and 7 respond to zero velocity echoes and numbers 2 through 6 provide for echoes having some velocity response. The VIP filter bank is preceded by an MTI canceller that is provided for canceling ground clutter by providing a deep symmetrical notch around zero Doppler frequency.
U.S. Pat. No. 4,622,552 to Andrews et al describes a Doppler processor which has a plurality of (N) transversal filters each of which are delayed by a delay circuit which delays a received signal by a time (T) which equals the interpulse period. The output of the Doppler processor is further filtered by a coherent integration filter to further reduce the level of the clutter components.
However, to date, no suitable method and device of tracking a target in clutter is available which effectively filters clutter from a reflected radar signal.
In accordance with the present invention, a method and a device is provided which effectively detects and tracks a target and filters clutter from a reflected radar signal. A feature of an embodiment of the present invention includes a method and a device which may identify a range extent of a cloud of clutter and calculate a centroid and growth rate of the cloud of clutter about the target in order to provide an effective filtering of the clutter from the reflected radar signal.
In accordance with one particular embodiment of the present invention, a method for discriminating and tracking a target in a clutter cloud comprises: transmitting a first radar signal at a first signal bandwidth for searching and locating a clutter cloud; transmitting a second radar signal at a second signal bandwidth to: identify a range extent of a clutter cloud; determine a centroid and a velocity growth rate of the clutter cloud; and identify a direction of movement of the centroid of the clutter cloud. The method may also comprise locking a third radar signal having a third signal bandwidth onto the centroid of the clutter cloud whereby the centroid is tracked within one radar range resolution bin; providing a delay line comprising at least two Doppler filters, the delay line may be configured to cover a Doppler frequency range corresponding to a velocity growth rate of the clutter cloud; and processing a reflected radar signal corresponding to the third signal bandwidth. The processing of the reflected radar signal may comprise passing the reflected radar signal through the delay line to mitigate a portion of the reflected signal that is reflected by the clutter cloud.
In accordance with another embodiment of the present invention, a radar system for tracking a target in a cloud of clutter may comprise a transmitter configured to selectively transmit a radar signal at a first radar bandwidth, at a second radar bandwidth, and at a third radar bandwidth. A receiver may be configured to receive a first reflected radar signal at the first radar bandwidth, a second reflected radar signal at the second radar bandwidth, and a third reflected signal at a third radar bandwidth. At least one processor may be interconnected with the receiver and the transmitter and may be configured to: locate a clutter cloud and target based on the first reflected radar signal; actuate the transmitter in order to lock the second radar signal at the second radar bandwidth onto the clutter cloud; identify a range extent of the clutter cloud and to calculate a centroid, a velocity growth rate and a direction of movement of the centroid of the clutter cloud based on the second reflected radar signal; actuate the transmitter in order to lock the third radar signal at the third radar bandwidth onto the centroid of the clutter cloud; provide a delay line comprising at least two Doppler filters, the delay line being configured to cover a Doppler frequency range corresponding to a velocity growth rate of the clutter cloud; and process the third reflected radar signal corresponding to the third radar bandwidth by passing the reflected radar signal through the delay line to mitigate a portion of the third reflected radar signal that is reflected by the clutter cloud.
In accordance with another embodiment, a processor for mitigating a clutter cloud in a reflected radar signal where the clutter cloud has a velocity growth rate may comprise an input for receiving a reflected radar signal and a delay line that comprises a plurality of moving target indicator (MTI) Doppler filters. The delay line may be configured to cover a Doppler frequency range corresponding to the velocity growth rate of the clutter cloud to mitigate a portion of a reflected radar signal that is reflected by the clutter cloud from the reflected radar signal. The processor also comprises an output connected in circuit with the plurality of MTI Doppler filters.
In accordance with a further embodiment, a method for discriminating and tracking a target in a clutter cloud comprises: transmitting a radar signal at a signal bandwidth to: identify a range extent of a clutter cloud; determine a centroid and a velocity growth rate of the clutter cloud; and identify a direction of movement of the centroid of the clutter cloud. The method may also comprise locking another radar signal having a greater signal bandwidth onto the centroid of the clutter cloud whereby the centroid is tracked within one radar range resolution bin; providing a delay line comprising at least two Doppler filters, the delay line being configured to cover a Doppler frequency range corresponding to a velocity growth rate of the clutter cloud; and processing a reflected radar signal corresponding to the greater signal bandwidth, the processing of the reflected radar signal comprising passing the reflected radar signal through the delay line to mitigate a portion of the reflected signal that is reflected by the clutter cloud.
In accordance with still a further embodiment, a radar system for tracking a target in a cloud of clutter comprises a transmitter that is configured to selectively transmit a radar signal at a first radar bandwidth and at a second radar bandwidth and a receiver that is configured to receive a first reflected radar signal at the first radar bandwidth and a second reflected radar signal at the second radar bandwidth. The system may also comprise at least one processor interconnected with the receiver and the transmitter that is configured to: identify a range extent of the clutter cloud and to calculate a centroid, a velocity growth rate and a direction of movement of the centroid of the clutter cloud based on the first reflected radar signal; actuate the transmitter in order to lock the second radar signal at the second radar bandwidth onto the centroid of the clutter cloud; provide a delay line comprising at least two Doppler filters, the delay line being configured to cover a Doppler frequency range corresponding to a velocity growth rate of the clutter cloud; and process the second reflected radar signal corresponding to the second radar bandwidth by passing the reflected radar signal through the delay line to mitigate a portion of the second reflected signal that is reflected by the clutter cloud.